Individual differences in male rat ejaculatory behaviour: searching for models to study ejaculation disorders

Authors

  • Tommy Pattij,

    1. Department of Anatomy and
    2. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute of Neurosciences, Utrecht University, Utrecht, the Netherlands
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    • *

      Present address: Research Institute Neurosciences VU, Center for Neurogenomics and Cognitive Research, Department of Medical Pharmacology, VU Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, the Netherlands.

  • Trynke R. De Jong,

    1. Department of Anatomy and
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  • Andre Uitterdijk,

    1. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute of Neurosciences, Utrecht University, Utrecht, the Netherlands
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  • Marcel D. Waldinger,

    1. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute of Neurosciences, Utrecht University, Utrecht, the Netherlands
    2. Department of Psychiatry and Neurosexology, Leyenburg Hospital, Den Haag, the Netherlands
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  • Jan G. Veening,

    1. Department of Anatomy and
    2. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute of Neurosciences, Utrecht University, Utrecht, the Netherlands
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  • Alexander R. Cools,

    1. Department of Psychoneuropharmacology, University Medical Center St Radboud, Nijmegen, the Netherlands
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  • Piet Hein Van Der Graaf,

    1. Department of Pharmacokinetics, Dynamics and Metabolism, Pfizer, Sandwich, UK
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  • Berend Olivier

    1. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute of Neurosciences, Utrecht University, Utrecht, the Netherlands
    2. Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
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Dr T. Pattij, at *present address below.
E-mail: t.pattij@vumc.nl

Abstract

In addition to investigating sexual function in rats that display normal ejaculatory behaviour, studying rats that are either ‘hyposexual’ or ‘hypersexual’ may provide important insights into the aetiology of ejaculatory dysfunctions in men, such as premature and retarded ejaculation. To this end, rats were matched into groups of ‘sluggish’, ‘normal’ and ‘rapid’ ejaculators based on their ejaculation frequencies displayed in a series of weekly sexual behaviour tests. Selecting rats on this parameter revealed large and stable differences in other parameters of sexual behaviour as well, including ejaculation latency and mount frequency but not intromission frequency and mount latency, putative indices of sexual motivation. Neuroanatomically, Fos immunoreactivity as a measure of neuronal activation was increased in rapid ejaculators compared with sluggish ejaculators in ejaculation-related brain areas, presumably associated with the differences in ejaculatory behaviour. Although the total number of oxytocin neurones within subregions of the hypothalamus did not differ between groups, in the supraoptic nucleus of the hypothalamus more oxytocin neurones were activated in rapid ejaculators compared with the other groups. Apart from the differences observed in ejaculatory behaviour, groups did not differ with respect to their locomotor activity and approach-avoidance behaviour as measured in the elevated plus-maze. Finally, apomorphine-induced stereotypy was similar in sluggish and rapid ejaculators, suggesting no large differences in dopamine susceptibility. Altogether, the present results suggest stable differences in male rat ejaculatory behaviour. Further exploring the neurobiological mechanisms underlying these differences may be a promising approach to gain insights into the aetiology of sexual dysfunctions such as premature, retarded or an-ejaculation.

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